IANAL repeat IANAL
Having said that, nothing stops any police department from arresting someone for frivolous things. In court, they will have to prove "Disorderly Conduct". Most departments who do this are counting on our ignorance of the law or our fear of the law and the courts. This charge would most likely be dismissed in court, since the state laws are pretty clear that carrying a fire arm is legal activity and there is nothing in the statute about disorderly conduct. They woujld most likely try to prove someone was alarmed. Hosever, just because someone is alarmed, does not mean anyone violated any laws. I am alarmed daily when I see the lunatics who drive in Seattle. Doesn't mean they will get into trouble over it.
In other words, the fella at the gunshop is blowing smoke up your shorts and if the local law enforcement make arrests for as you describe, they are in violation of several state laws and are in need of education. You can always download the training bulletins and other documents that are available in this forum (do a search in the Washington Forum for "Constitution") and anonymously mail. Better yet, let them know who you are when you mail them so that if they confront you, you are already on record as knowing your rights and the law.
Anyway, as I said before... IANAL